1. Field of the Invention
The invention at hand relates to a method for controlling a number of machining processes on a die-sink erosion machine and a device suitable for this purpose.
2. Description of Related Art
Such a die-sink erosion machine is used, among other purposes, for manufacturing casting molds with extremely high machining precision. Hereby a number of machining processes which themselves are divided into several working steps and working cycles of different machining stages or phases are performed on one or more workpieces. Depending on the machining phase, such as roughing or finishing, often different electrode categories, such as, for example, roughing or smoothing electrodes, are used for performing these machining processes. If, in addition, the geometry of the performed machining job changes, the electrode must be exchanged in most cases also. This means that depending on the number, versatility, and quality requirements of the machining processes to be performed in a modern die-sink erosion machine, the order of the work steps to be performed and the electrodes required in each case requires an exact specification that is stored in a control program of a numerical control of the die-sink erosion machine.
When setting up the die-sink erosion machine for such a complex machining job, the machine operator must set the control inputs in the control device that determine which work-steps of a machining process must be performed in which sequence with which electrode on which workpiece. Standard, state-of-the-art control processes of the initially mentioned type require control inputs in the form of closed xe2x80x9cprogramsxe2x80x9d, so-called sequential control programs, for this purpose. Such a control program specifies all control data in respect to machining, machining frequency, and electrode used for each point in time during the overall machining. Given the multiple work steps in a complex machining of several workpieces that must be performed and the different electrodes necessary for this purpose, the machine operator easily loses track, so that setup errors could occur that would result in an improper, but at least uneconomical execution of the machining.
The state of the art indeed knows of methods for the so-called object-oriented programming of machine tools, for example from Prof. Dr. Ing. Eversheim, Dipl.-Ing. Lenhart, Objektorientiert Programmieren, in: Industrie-Anzeiger 82/1991, p. 38-40. In contrast to sequential control programs, program components are used here that can be reused over and over again for changing the control program. Hereby only an object-oriented structure of the source program is suggested. But no tool for creating certain machining sequences is made available to the machine operator.
The invention at hand attempts to improve die-sink erosion machines in respect to their user friendliness where the creation of new machining sequences is concerned.
According to one aspect of the present invention, a method controls multiple machining processes in a die-sink erosion machine with several identical or different electrodes, whereby the machining sequence of the machining processes and the electrode used for each machining process are determined with consideration of the following predefined criteria: a) predefining priorities of workpieces to be machined, of a group of machining jobs, of individual machining jobs, of work cycles and/or work steps of a machining job; and/or (b) predefining the life span or wear limit of the electrodes used for the individual machining jobs, work cycles or work steps. The overall machining on the die-sink erosion machine is performed with consideration of the determined machining sequence. To create the machining sequences, a device according to one aspect of the invention for controlling the die-sink erosion machine has, for example, a CNC controller: at least one data memory for the permanent storing of data describing the electrodes required for the respective machining processes; a user interface for inputting the previously mentioned criteria for determining the machining sequence into the control device; and a sequence generator that automatically generates the suitable machining sequence for the performing the multiple machining processes based on said criteria and electrode data.
The invention therefore offers the machine operator a proven tool for setting even complicated machining sequences on a die-sink erosion machine in a relatively simple manner and short time. The creation of the sequence and therefore also of the control program and the subsequent machining also takes into account tool wear, for example, by predefining the tool life span as the maximum number of possible work cycles for each machining type, for example for roughing and smoothing cycles. Once the predefined wear limit of a tool is reached, a tool administration or management system according to one aspect of the invention preferably excludes the tool from further machining or downgrades it to a different tool category, as will be described in more detail below. In this way, the selection of the favorable machining sequence according to the invention is based on the fact that the available electrode material is optimally used, i.e., each electrode is used for several machining processes with or without interruption until its individual life span expires. Another outcome of predefining suitable machining priorities is also that a certain object will be machined before another object is completed. It would be possible, for example, that a certain workpiece would need to be machined with a higher priority because a customer needs this workpiece immediately, or a specific, complicated machining job is moved ahead so that in the case of a failure a workpiece which was already machined with great effort is not lost. A specific predefining of priorities also makes it possible to perform several machining jobs in as little time as possible, and to minimize any traveling distances between machining jobs during which no erosion is possible as much as possible.
The method according to one aspect of the invention and the corresponding device naturally can be transferred to other types of machine tools in which comparable wear symptoms of the used tools occur and/or similar machining priorities can be used.
The term xe2x80x9cmachining processxe2x80x9d has been used in this document as a general term comprising all parts of the work performed on a die-sink erosion machine. This includes the execution of a particular die-sink with a predefined die-sink geometry which is called a xe2x80x9cmachining jobxe2x80x9d. Each machining job is performed in several machining steps or phases, for example, in consecutive order, roughing, pre-smoothing, smoothing, and finishing. In each machining phase, a machining job again consists of several work steps that may be combined into so-called work cycles. The term xe2x80x9cmachining sequencexe2x80x9d therefore in general relates to the order of the consecutively performed machining processes which, depending on the type of machining process, may be the order of consecutively performed machining jobs, work cycles of several machining jobs and/or work steps in a work cycle of a certain machining job or combinations of these sequences.
An especially preferred embodiment of the method uses the so-called wear distribution strategy as a selection criterion for performing several identical machining jobs. The individual machining jobs are hereby not completed in their respective entirety, one after the other, but the consecutively performed machining processes are instead distributed in such a way over several machining jobs that an even distribution of the electrode wear over a certain number of work cycles and/or work steps of the multiple machining jobs is obtained. It is known that a sinker electrode experiences electrode wear during the machining, which can be attributed to the electrophysical nature of the erosion process so that the sinker electrode wears after performing a certain number of work steps. Therefore, in order to maintain the most homogeneous machining quality possible for all machining jobs, it is advantageous to perform all identical or equally ranked working steps of multiple machining jobs consecutively, for example, starting with all first work steps of the multiple machining jobs, then all second work steps, etc., until all of the last work steps of the multiple machining jobs have been performed.
In this connection, the multiple, identical machining jobs of a wear distribution area are preferably performed consecutively in a certain order, for example 1-2-3-4, and after a first (1) or last (4) machining job are repeated in reverse order, i.e., 4-3-2-1, until all work steps of the machining jobs have been performed. This embodiment of the wear distribution strategy avoids that one machining job is machined with privileges over another. As a result, the wear distribution strategy makes it possible that all identical machining jobs are eroded equally well (or equally poorly). In the proposed embodiment, the electrode quasi moves in xe2x80x9cpendulumxe2x80x9d fashion through the rows of equally ranked work steps of several machining jobs, from the first to the last machining job, from the last to the first, etc., until all work steps of the machining jobs have been completed (so-called pendulum method), so that all machining jobs are completed very quickly.
It is also preferred that the maximum electrode wear of an electrode is defined by the maximum number of work cycles or work steps that can be completed with this electrode, whereby this number at the same time determines the group of work cycles or work steps in which the wear distribution strategy is used. In this manner, several work cycles of a certain machining phase are, for example, combined into so-called wear distribution groups which are in each case machined only with a single electrode. After the wear distribution group has been completed, the life span of this electrode for the respective machining phase has expired. This ensures in a particularly clear manner that all electrodes are used completely.
The machining sequence in such a wear distribution group again can be set according to the wishes of the machine operator, for example, preferably so that only selected areas of work steps in a group of work cycles are included in the wear distribution strategy. Only the last two work steps in several work cycles of several machining jobs that were combined into a wear distribution group are supposed to use an even distribution of the wear of the used electrode, preferably in a pendulum method, as mentioned above.
The information on the life span of an electrode of the die-sink erosion machine, i.e., the maximum number of work cycles or work steps of a certain machining phase for which an electrode can be used and the current wear status can be obtained in various ways. In the case of a die-sink erosion machine in which several machining jobs, each of which has several work cycles, are performed consecutively, the maximum electrode wear is preferably predefined for use in an electrode administration system using the maximum number of work cycles or work steps that can be performed with one electrode, and the electrode administration system counts and registers the number of performed work cycles or work steps during the machining. The information regarding the electrode life span makes it possible to set up an automatic electrode administration or electrode management system in the controller of the die-sink erosion machine. If a certain electrode has reached the predefined wear limit, it is automatically excluded by the administration system from further machining or is assigned to another machining phase, i.e., to another electrode category for which this electrode can still be used. The entire electrode administration takes place via an intelligent CNC controller of the machine.
It is preferred that the electrodes are described in the administration system of the control device by way of a current machining status, whereby the latter is adapted during the course of the machining in relation to the electrode wear. The electrode administration according to the invention therefore monitors the wear status of the used electrodes which are, for example, available in an electrode changer, and assigns to them storage status properties, such as xe2x80x9cusablexe2x80x9d, xe2x80x9cunusablexe2x80x9d or xe2x80x9cdowngraded to roughing electrodexe2x80x9d, etc.
To perform a machining sequence, the controller also needs detailed information about the electrodes used in each work step of the machining sequence. According to an especially preferred exemplary embodiment, the data for describing the electrodes in the control device are divided for this purpose into the following groups and administered accordingly:
abstract electrode data for describing a standard electrode (V1, V2) that contain information for performing a certain machining process; and,
specific electrode data for correcting and/or adapting the abstract electrode data to the actually used electrode (R1, R2) or to machine-specific characteristics,
whereby the electrode description is obtained by linking the abstract electrode data with the specific electrode data.
The abstract electrode data already contain all essential information about the electrode(s) planned for performing a specific (individual) machining job in a specific type of machining. This is a description of standard or specified electrodes required for performing a specific, desired machining job, whereby this abstract description also contains all machining-specific information of the electrode, for example the basic electrode geometry, the basic electrode shape, the electrode material, the electrode category, for example whether it is a roughing or a smoothing electrode. The specific electrode data then contain only the correction data, for example in respect to the exact dimension of the actually used electrode, such as the actual, smaller than specified size which may differ from the (assumed) smaller than specified size of the prescribed tool, as well as machine-specific data, such as, for example, the exact chucking position of the electrodes, the current position in an electrode magazine for an automatic electrode change and/or the current wear status of the actually used electrode, as it is registered in the above mentioned administration system. The idea is therefore to generalize the electrode description, i.e., to abstract it in the description of a standard tool independently from the actually encountered situation in the die-sink erosion machine and the real electrodes used, so that the electrode description can already be performed before the actual machining, outside the workshop. It is preferred that an intelligent data generator automatically determines the machining sequence with the technology and process parameters of individual work steps of the desired machining job on the basis of the abstract electrode data together with the sequence selection criteria according to the invention and geometrical data and technology and process parameter sets available in databases.
Another criterion for selecting and determining the machining sequence is the predefining of priorities. There are different preferred possibilities for adapting the desired machining sequence to the corresponding circumstances for this purpose.
In one embodiment, the machining sequence is determined as a matter of priority by the priorities assigned to the workpieces, groups of machining jobs, and individual machining jobs within a group (xe2x80x9cworkpiecexe2x80x9d strategy). The machining job with the highest priority in the group is hereby performed first on the workpiece with the highest priority, from the first work step to the last one. Hereby no wear distribution is employed for the used electrode, since only one machining job is always performed after another, i.e., the machining processes are not distributed over several machining jobs. It is preferred that with the xe2x80x9cworkpiecexe2x80x9d strategy the electrode wear is actively counted, whereby, for example, the respective electrode is assigned the storage status xe2x80x9cunusablexe2x80x9d in the electrode administration after the wear limit has been reached.
In another embodiment, the machining sequence of machining jobs performed in several machining steps or phases, such as, initially, roughing, then pre-smoothing, etc., and where in each machining phase the work steps of a single machining job in each case have been combined into work cycles, is determined as a matter of priority by the fact that all work steps of all machining jobs are performed in the predefined hierarchy of the machining phases. For example, in the case of several die-sinks, first all work steps of the roughing cycles, then all work steps of the pre-smoothing cycles, etc., are performed. Depending on the desired machining quality, this strategy also distinguishes: (a) the xe2x80x9cphasexe2x80x9d strategy, in which all work steps in each machining phase are performed consecutively from start to finish of a machining job, then all work steps of the next machining job are performed from start to finish, etc., until the last machining job of the same machining phase has been performed; and (b) the xe2x80x9cphase 0xe2x80x9d strategy, in which initially all first work steps of several machining jobs of the same machining phase are performed, and then, based on the last machining completed, the remaining work steps of the machining jobs are completed as described for the xe2x80x9cphasexe2x80x9d strategy. Because these xe2x80x9cphasexe2x80x9d and xe2x80x9cphase 0xe2x80x9d strategies distribute the machining sequence in a specific machining phase over several machining jobs, it is particularly advantageous to additionally use the above described wear distribution strategy here. For example, given a specific wear limit of an electrode type, such as the roughing electrode, a wear distribution group consisting of, for example, four roughing cycles distributed over four identical machining jobs, is formed. Within this wear distribution group it is also possible to limit the wear distribution function only to the first two work steps per cycle, and to use the progression of the xe2x80x9cphase 0xe2x80x9d strategy for the remainder.
Other possibly advantageous embodiments include those in which the machining sequence is assigned as a matter of priority according to the priority of a workpiece and the strategy specified for the workpiece (xe2x80x9cpiecexe2x80x9d strategy), or as a matter of priority according to the priorities assigned to the individual work steps (xe2x80x9cwork stepxe2x80x9d strategy). The latter makes it, for example, possible to set the machining sequence to the lowest level of the machining processes, so that the machine operator is also able to predefine individual sequences of work steps for the control device.
It is also especially preferred that combinations of the mentioned strategies, such as of the xe2x80x9cworkpiecexe2x80x9d strategy and the xe2x80x9cphasexe2x80x9d or xe2x80x9cphase 0xe2x80x9d strategy are used.
In a first combination embodiment, the machining sequence is as a matter of priority determined by the xe2x80x9cworkpiecexe2x80x9d strategy, whereby the workpieces, groups or machining jobs are completed with same priority using the xe2x80x9cphasexe2x80x9d or xe2x80x9cphase 0xe2x80x9d strategy (so-called xe2x80x9cworkpiece-phasexe2x80x9d or xe2x80x9cworkpiece-phase 0xe2x80x9d strategy). This combined strategy is suitable in particular in connection with a xe2x80x9ccascade-typexe2x80x9d downgrading of the used electrodes, whereby those electrodes used, for example, in a work cycle of a high phase, for example a smoothing cycle of the machining job with the highest priority, can still be used for machining jobs of lower priority after the expiration of their life span for one or more work cycles of a lower phase, for example, a roughing cycle. If, in addition, a wear distribution strategy is desired for the work cycles to be performed, the former naturally can be set for machining jobs with the same priority.
In a second combination embodiment (xe2x80x9cphase-workpiecexe2x80x9d or xe2x80x9cphase 0-workpiecexe2x80x9d strategy), the machining sequence is influenced according to the xe2x80x9cphasexe2x80x9d or xe2x80x9cphase 0xe2x80x9d strategy to the extent that the sequence of work steps and possibly the order of the division of the wear distribution groups take into account the priority of the machining jobs according to the xe2x80x9cworkpiecexe2x80x9d strategy.